Style.css won’t link to pages

So I’ve been moving my html and css onto wordpress for a website.
I followed this youtube video:

And it’s gone ok, but the style.css page is not working with any of my pages :-/
Help pretty please internet people!
Just ask if I can give more info to help, I am very new to all this so not that sure what info I should be presenting to make it solvable.

<p>David Kirkman, who lives in South Somerset, is a qualified R4 Tennis Referee who organises an extensive range of tennis tournaments in/around the South Somerset area. The tournaments organised range from Grade 4 to Grade 6; with events for minis, Boys/Girls and Adults some doubles also offered.</p>

<p>David is known as a proactive promoter and has very successful tournaments, normally with good entry numbers due to the increased likelihood that they will run along with the repeat support from many satisfied players/parents. David is a flexible organiser and will often take Late Entries (if room in the draw, court time available) especially before the draw Is made.</p>

<p>David started refereeing back in 2012, to try and both promote tennis and get more tennis opportunities for his 15-year old son; so often looks at It from the perspective of a player/parent. Due to its success, David has been requested by various venues to run tournaments for them … also subsequently tasked by the SSTDG to organise/promote all of their tournaments so you will find him on court somewhere about 40 days each year.</p>

<p>If resident in, within travelling distance of or just visiting the South Somerset area, then hopefully one of the Forthcoming Tournaments listed below (or one from the Seasonal Spreadsheet) will be of interest to you.</p>

<p>Keep enjoying your tennis and we look forward to seeing you at a tournament soon.</p>